Thermoplastic compositions are actively pursued for use in rotational molding processes, such as slush molding, as an alternative to typical thermoforming processes to fabricate articles of manufacture. In the automotive field, thermoplastic compositions have been used for the fabrication of articles such as interior sheathing, used for instrument panel skins, door panels, air bag covers, roof liners and seat covers.
Many of the articles have surface appearances and designs having complex surface characteristics, such as contours and geometric technical grains, and may be produced in a slush molding process. However, other material properties such as strength and low shear viscosity desired for slush molding processing are difficult to achieve with current thermoplastic compositions. Current thermoplastic compositions, such as thermoplastic polyolefin and thermoplastic polyurethane, are often processed for prolonged time periods at high temperatures to form fused skins in a slush molding process. The compositions of such thermoplastic materials may degrade during processing, however, which in turn may alter the material properties, such as the strength of the material and the uniform fusion of the composition. As a result, articles produced using thermoplastic compositions may have unacceptable surface appearance and mechanical properties.
Thus, there is a need in the art for a thermoplastic composition with low near zero shear viscosity at molding temperatures for use in slush molding to achieve acceptable surface appearance while maintaining other material properties such as tensile strength. In addition, there is a need in the art for a method for preparing a thermoplastic composition with improved properties such as uniform melt fusion and heat conductivity for use in the fabrication of articles with improved surface skin characteristics. There is a still further need to convert the composition into a suitable powder (avg. particle size in the range of about 75 μm to about 400 μm) and/or micropellet form (avg. particle size in the range of about 300 μm to about 900 μm), with good mechanical flow during the slush molding process. There is a further need in the art for a process for preparing such a composition for use in manufacturing automotive and non-automotive articles of manufacture.